With increasing high functionalization and miniaturization of semiconductor packages which are widely used for electronic equipment, communication apparatuses, and personal computers or the like, in recent years, high integration and high-density packaging have been increasingly accelerated. As a result, requirements to a laminate used for the semiconductor package are also various, and characteristics such as flame retardance and low water absorption according to standardization of halogen-phosphorus free, lead free of solder are required from consideration to environmental problems.
It has been known that a coefficient of thermal expansion in the plane direction of the laminate at a temperature higher than a glass transition point is different from that at a temperature lower than the glass transition point, and the coefficient of thermal expansion is decreased immediately after exceeding the glass transition point. Because a plastic package is heated to 260° C. or more by solder reflow processing or the like in a producing process, the difference between the coefficients of thermal expansion in the plane direction is increased between the laminate and a sealing resin or the like by the declination of the coefficient of thermal expansion described above when the glass transition temperature of the laminate is low, which causes production faults such as warpage. Therefore, a high glass transition temperature is required for the laminate. In order to suppress a shape change caused by the coefficient of thermal expansion of the sealing resin, a high elastic modulus at high temperature is also required.
In a technique of raising the glass transition temperature of the laminate, an ingredient having a high glass transition temperature is used for a resin composition for the laminate (for example, see Patent Literature 1). Novolac-based bismaleimide is used as the resin ingredient raising the glass transition temperature in Patent Literature 1. However, because the glass transition temperature of other resin ingredient is low, it is difficult to attain the glass transition temperature of 260° C. or more. In order to attain the glass transition temperature of 260° C. or more, it is necessary to increase the amount of an inorganic filler used. In this case, the moldability is easily predicted to be poor.
As another technique, the blending of a cyanate ester resin and bismaleimide has been known. Many case examples using a novolac-based cyanate ester resin particularly as a cyanate ester compound can be found (for example, see Patent Literature 2). However, the novolac-based cyanate ester resin is apt to be insufficiently cured in a normal curing condition. The obtained cured product disadvantageously has a large water absorption ratio.